Cholesterol (cont.)
What are triglycerides, chylomicrons, and VLDL?
Triglyceride is a fatty substance that is composed of three fatty acids. Like cholesterol,
triglyceride in the blood either comes from the diet or the liver. Also, like
cholesterol, triglyceride cannot dissolve and circulate in the blood without
combining with a lipoprotein. Thus, after a meal, the triglyceride and
cholesterol that are absorbed into the intestines are packaged into round
particles called chylomicrons before they are released into the blood
circulation.
A chylomicron is a collection of cholesterol and triglyceride that is
surrounded by a lipoprotein outer coat. (Chylomicrons contain 90% triglyceride
and 10% cholesterol.)
The liver removes
triglyceride and chylomicrons from the blood, and it synthesizes and packages
triglyceride into VLDL (very low-density lipoprotein) particles and releases
them back into the blood circulation.
Do high triglyceride levels cause atherosclerosis?
Whether elevated triglyceride levels in the blood lead to atherosclerosis and
heart attacks is controversial. While most doctors now believe that an
abnormally high triglyceride level is a risk factor for atherosclerosis, it is
difficult to conclusively prove that elevated triglyceride by itself can cause
atherosclerosis. However, it is increasingly recognized that elevated
triglyceride is often associated with other conditions that increase the risk of
atherosclerosis, including obesity, low levels of HDL- cholesterol, insulin
resistance and poorly controlled diabetes mellitus, and small, dense LDL
cholesterol particles.
What are the causes of elevated triglyceride levels?
In some people, abnormally high triglyceride levels (hypertriglyceridemia)
are inherited. Examples of inherited hypertriglyceridemia disorders include
mixed hypertriglyceridemia, familial hypertriglyceridemia, and familial
dysbetalipoproteinemia.
Hypertriglyceridemia can often be caused by non-genetic factors such as
obesity, excessive alcohol intake, diabetes mellitus, kidney disease, and
estrogen- containing medications such as birth control pills.
How can elevated blood triglyceride levels be treated?
The first step in treating hypertriglyceridemia is a low fat diet with a
limited amount of sweets, regular aerobic exercise, loss of excess weight,
reduction of alcohol consumption, and stopping cigarette smoking. In patients
with diabetes mellitus, meticulous control of elevated blood glucose is also
important.
When medications are necessary, fibrates (such as Lopid), nicotinic acid, and
statin medications can be used. Lopid not only decreases triglyceride levels but
also increases HDL cholesterol levels and LDL cholesterol particle size.
Nicotinic acid lowers triglyceride levels, increases HDL cholesterol levels and
the size of LDL cholesterol particles, as well as lowers the levels of Lp (a)
cholesterol.
The statin drugs have been found effective in decreasing
triglyceride as well as LDL cholesterol levels and, to a lesser extent, in
elevating HDL cholesterol levels. A relatively new medicine, fenofibrate
(Tricor), shows promise as an effective agent in lowering serum triglyceride
levels as well as raising HDL levels, particularly in patients who have had
suboptimal responses to Lopid. In some patients, a combination of Lopid or
Tricor with adjunctive statin therapy (see below) may be prescribed. While this
combination is often effective in patients with complex lipid disorders, the
potential for side effects may be increased and such patients should be under
strict medical supervision.
What are lipid-altering medications?
Lipid altering medications are used in lowering blood levels of undesirable
lipids such as LDL cholesterol and triglycerides and increasing blood levels of
desirable lipids such as HDL cholesterol. Several classes of medications are
available in the United States, including HMG CoA reductase inhibitors
(statins), nicotinic acid, fibric acid derivatives, and medications that
decrease intestinal cholesterol absorption (bile acid sequestrants and
cholesterol absorption inhibitors). Some of these medications are primarily
useful in lowering LDL cholesterol, others in lowering triglycerides, and some
in elevating HDL cholesterol. Medications also can be combined to more
aggressively lower LDL, as well as in lowering LDL and increasing HDL at the
same time.
Lipid altering medications commonly used in the United States
| Medication class |
Medication examples |
Effects on blood lipids |
| statins |
Pravachol, Mevacor, Lipitor, Lescol, Crestor, Zocor |
Most effective in lowering LDL, mildly effective in
increasing HDL, mildly effective in lowering triglycerides |
| Nicotinic acid (Niacin) |
Niacin, Niaspan, Slo-Niacin |
Most effective in increasing HDL, effective in lowering
triglycerides, mildly to modestly effective in lowering LDL |
| Fibric acid |
Lopid, Tricor |
Most effective in lowering triglycerides, effective in
increasing HDL, minimally effective in lowering LDL |
| Bile acid sequestrants |
Questran, Welchol, Colestid |
Mildly to modestly effective in lowering LDL, no effect on
HDL and triglycerides |
| Cholesterol absorption inhibitors |
Zetia |
Mildly to modestly effective in lowering LDL, no effect on
HDL and triglycerides |
| Combining nicotinic acid with statin |
Advicor
(lovastatin+niaspan) |
Effective in lowering LDL and triglycerides and increasing HDL |
| Combining a statin with an absorption inhibitor |
Vytorin (Zocor + Zetia) |
Synergistic in lowering LDL and effective in lowering LDL with low doses of each
ingredient |
Next: What are the statin drugs? »
- simvastatin, Zocor - Read about the medication simvastatin (Zocor) a cholesterol- lowering drug used to inhibit the production of cholesterol by the liver. Article includes descriptions, uses, drug interactions, and side effects.
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